chore!(amneziawg): refactor to be separate from wireguard

- amneziawg is now a VPN protocol and no longer a Wireguard implementation
- Use it with VPN_TYPE=amneziawg
- document AMNEZIAWG_* options in Dockerfile
- document amneziawg support in readme
- separate amneziawg settings and code from wireguard
- re-use code from wireguard whenever possible

internal/amneziawg/log.go

@@ -0,0 +1,11 @@
+package amneziawg
+
+//go:generate mockgen -destination=log_mock_test.go -package amneziawg . Logger
+
+type Logger interface {
+	Debug(s string)
+	Debugf(format string, args ...interface{})
+	Info(s string)
+	Error(s string)
+	Errorf(format string, args ...interface{})
+}